1. Field of the Invention
The present invention relates to a radio signal transceiver apparatus, and more particularly it relates to a transceiver apparatus capable of achieving an improvement in linearity in code division multiple access (CDMA) systems.
2. Description of the Related Art
Generally, transmitting and receiving systems for radio signals are classified into those of the analog type and those of the digital type. Recently, digital transmitting and receiving systems have mainly been used for radio signals, by virtue of rapid developments of techniques. A representative of such digital systems is a CDMA system. Now, signal transmitting and receiving procedures conducted in a transceiver apparatus of such a digital system will be described.
First, the receiving procedure will be described. An input signal received via an antenna is amplified by a low noise amplifier. The amplified signal is then filtered in order to extract components of a usable band therefrom. The filtered signal is then down converted to an intermediate frequency by a down mixer. The resultant signal is filtered again in order to eliminate unnecessary waves, generated during the down conversion, therefrom. The input signal, which has been filtered at the intermediate frequency, is amplified again and then sent to a demodulator, which, in turn, demodulates the received signal. The demodulator sends the demodulated signal to a digital signal processor (DSP) which, in turn, checks the intensity of the received signal, thereby adjusting the degree of receiving amplification and the degree of transmitting amplification. In such a configuration, however, the down mixer, which conducts a down conversion to the intermediate frequency, may operate abnormally. That is, where a high-intensity signal not intended, for example, an analog cellular signal, is received in the low noise amplifier, the down mixer may be saturated, so that it operates abnormally.
Next, the transmitting procedure will be described. The DSP determines the degree of desired transmitting amplification in accordance with the level of receiving power and sends a signal, to be transmitted, to a modulator which, in turn, modulates the signal. The modulated signal from the modulator is amplified and then filtered to eliminate pseudo components thereof generated during modulation. The filtered signal is converted to a transmitting frequency by an up mixer. The resultant signal from the up mixer is then filtered again to eliminate unnecessary components thereof generated during the conversion to the transmitting frequency. The resultant filtered signal is sent to a drive amplifier which, in turn, amplifies the received signal to a transmitting power level. The degree of amplification of the drive amplifier is set to a fixed value. For this reason, when the transmitting amplifier, which amplifies the modulated signal at the transmitting stage, is adjusted to increase its degree of amplification in order to ensure an interference between adjacent channels required in the CDMA system when the channel is in a degraded state, it may generate a signal amplified in excess of the maximum amplification level of the drive amplifier. In other words, an over amplification may occur in the drive amplifier. In such a case, there is a degradation in the linearity of the signal output from the drive amplifier. Moreover, when such a signal, which is excessively amplified, is output after being amplified by the transmitting amplifier and drive amplifier, a large waste of current is generated because the entire degree of amplification is very high. This results in a reduction in communication time in portable phones.
Accordingly, an object of the present invention is to provide a transmitter apparatus in a CDMA system which includes a drive amplifier capable of achieving an improvement in linearity.
Another object of the invention is to provide a receiver apparatus in a CDMA system which includes a down mixer configured not to be saturated during a conversion operation thereof to an intermediate frequency.
Another object of the invention is to provide a transmitter apparatus in a portable phone capable of reducing the consumption of current.
In accordance with the present invention, these objects are accomplished by providing a transceiver apparatus in a code division multiple access system comprising: a low noise amplifier for amplifying a signal received via an antenna; a first filter for extracting components of a usable band from said signal amplified by said low noise amplifier; a voltage controlled amplifier for amplifying said signal filtered by said first filter; a down mixer for converting said signal amplified by said voltage controlled amplifier to an intermediate frequency; a second filter for eliminating unnecessary waves, generated during said conversion operation of said down mixer, from said signal converted by said down mixer; an automatic gain controlled amplifier for amplifying said signal filtered by said second filter; a demodulator for demodulating said signal amplified by said automatic gain controlled amplifier; and a control unit for receiving said signal demodulated by said demodulator, and determining an amplification degree of each of said amplifiers in accordance with the power level of said received signal, and outputting control signals respectively adapted to determine the degree of amplification and whether or not amplification should be conducted in a drive amplifier, in accordance with the power level of said received signal, said control unit also outputting a signal to be transmitted. A modulator modulates said signal, to be transmitted, received from said control unit, and an amplifying unit amplifies said signal modulated by said modulator at the degree of amplification determined by said control unit. A third filter eliminates noise components from said signal amplified by said amplifying unit, and an up mixer converts said signal filtered by said third filter to a transmitting band frequency. A fourth filter eliminates unnecessary wave components from said signal converted to said transmitting band frequency. The drive amplifier received said control signal adapted to determine whether or not an amplification should be conducted in said drive amplifier, and amplifies said signal filtered by said fourth filter or served as a transmitting path for said signal filtered by said second filter, in accordance with said control signal received therein.